The present invention relates to a semiconductor device having a bump electrode and a method of manufacturing the same.
Bump electrodes are generally formed in the art at positions around the chip periphery at which semiconductor chips are not formed. The chip is bonded by means such as thermal pressure by tape automated bonding (TAB) techniques, by way of example. With TAB, there is a possibility of a crack of the chip in the vicinity of the underneath of the bump electrodes, due to stresses imparted to the chip through the bump electrodes during the thermal pressure. The general procedure is therefore to form the bump electrodes 8 for bonding so that they are disposed around the periphery of the chip, and not form and bump electrodes in a region 10 in which the semiconductor chips are formed (the active surface), as shown by way of example in FIG. 10. If bump electrodes are formed around the periphery of the chip, however, the surface area increases and a technical problem arises in that it is not possible to make the chip smaller.
To prevent a crack of such a chip in this case, techniques are known of providing the semiconductor device with a buffer material for mitigating thermal stresses and impact stresses due to the heating and impact applied during the bonding (Japanese Patent Laid-Open No. 5-55228 and Japanese Patent Laid-Open No. 6-151436). The configuration of the bump electrode of Japanese Patent Laid-Open No. 5-55228 is shown in FIG. 12.
First there is a silicon substrate 21 on which is formed aluminum wiring (an electrode) 22. A silicon nitride film (insulating protective layer) 23 is formed thereabove, to protect the electrode. An aperture portion 26 is formed in the silicon nitride film 23, extending as far as the aluminum wiring 22. A polyimide film 25 is formed over the silicon nitride film 23 as a buffer layer. An aperture portion 27 is formed in the polyimide film 25, extending as far as the aluminum wiring 22. The aperture portion 27 formed in the polyimide film 25 is formed on the inner side of the aperture portion 26 in the silicon nitride film 23. The side surface of the aperture portion 26 is therefore covered by the polyimide film 25. A titanium film 24 is formed over the polyimide film 25, the side surface of the aperture portion 27, and the aluminum wiring 22 as an under electrode. A copper film 30 is formed over the titanium film 24. A copper plated film 28 is formed over the copper film 30. A gold plated film 29 is formed over the copper plated film 28.
A bump electrode 31 that is formed of this gold plated film 29 and the copper plated film 28 is subjected to bonding loads due to forces such as thermal pressure during the bonding, but the polyimide film 25 can act as a buffer layer to mitigate stresses applied during the bonding to the lower surface of the bump electrode 31 that is in contact therewith through the titanium film 24. As a result, it is possible to prevent a crack of the silicon nitride film 23 that acts as the insulating protective film, enabling a reduction in damage to the chip.
Japanese Patent Laid-Open No. 6-151436 has a bump electrode of a mushroom shape that is similar to that of Japanese Patent Laid-Open No. 5-55228, where a polyimide is formed as a buffer film in a cavity portion of this umbrella shape. The effect of this configuration of the bump electrode also makes it possible to prevent a crack of the protective insulating film of the electrode, in a similar manner to Japanese Patent Laid-Open No. 5-55228.
However, there is a danger in the configurations of both Japanese Patent Laid-Open No. 5-55228 and Japanese Patent Laid-Open No. 6-151436 that the fat “neck” portion of the mushroom shape could cause a crack of the elements, even though the buffer film mitigates impact loads due to factors such as thermal pressure during bonding. If the material of the neck portion of the bump electrode has a hardness on the order of copper, the impact loads applied during bonding are even more likely to be transferred directly to the elements.
In addition, the manufacturing method of Japanese Patent Laid-Open No. 5-55228 necessitates an extra step of forming a photoresist film when forming the aperture portion 26 or the aperture portion 27 in the polyimide film 25 that acts as a buffer film of the silicon nitride film 23 that protects the electrode.